cli-highlight

What is cli-highlight?

The cli-highlight npm package is a syntax highlighter for the command line. It takes code as input and outputs it with syntax highlighting, making it easier to read and understand. It supports a wide range of programming languages and can be used both as a command-line tool and as a library in Node.js applications.

What are cli-highlight's main functionalities?

Syntax highlighting in the terminal

This feature allows you to highlight syntax of code snippets directly in the terminal. The code sample demonstrates how to use the highlight function from the cli-highlight package to syntax highlight a JavaScript code snippet.

const highlight = require('cli-highlight').highlight;
console.log(highlight('const x = 1;', {language: 'javascript', theme: 'default'}));

Highlight code from a file

This feature allows you to read code from a file and output it with syntax highlighting in the terminal. The code sample shows how to read a JavaScript file and use the highlight function to apply syntax highlighting.

const highlight = require('cli-highlight').highlight;
const fs = require('fs');

fs.readFile('example.js', 'utf8', (err, code) => {
  if (err) throw err;
  console.log(highlight(code, {language: 'javascript', theme: 'default'}));
});

Use as a command-line tool

cli-highlight can also be used as a standalone command-line tool. This code sample demonstrates how to use cli-highlight to highlight a JavaScript file named 'example.js' using the default theme.

highlight -l javascript -t default example.js

Other packages similar to cli-highlight

chalk

Chalk is a popular npm package for styling terminal strings. Unlike cli-highlight, which is focused on syntax highlighting, Chalk allows you to apply custom styles like colors, background colors, and text styles to strings in the terminal.

pygmentize-bundled

pygmentize-bundled is an npm package that provides syntax highlighting by wrapping the Python Pygments library. It offers a wide range of languages and styles, similar to cli-highlight, but requires Python to be installed on the system.

cardinal

Cardinal is another syntax highlighter for JavaScript code that can be used in the terminal. It is similar to cli-highlight but is specifically designed for JavaScript and includes features like line numbers and custom themes.

README

cli-highlight

Syntax highlighting in your terminal

Example

CLI Usage

Output a file

$ highlight package.json

Color output of another program with piping. Example: A database migration script that logs SQL Queries

$ db-migrate --dry-run | highlight

Command line options:

Usage: highlight [options] [file]

Outputs a file or STDIN input with syntax highlighting

Options:
  --language, -l  Set the langugage explicitely
                  If omitted will try to auto-detect
  --theme, -t     Use a theme defined in a JSON file
  --version, -v   Show version number                                   [boolean]
  --help, -h      Show help                                             [boolean]

Programmatic Usage

You can use this module programmatically to highlight logs of your Node app. Example:

const highlight = require('cli-highlight').highlight
const Sequelize = require('sequelize')

const db = new Sequelize(process.env.DB, {
  logging(log) {
    console.log(highlight(log, {language: 'sql', ignoreIllegals: true}))
  }
})

Detailed API documenation can be found here.

Themes

You can write your own theme in a JSON file and pass it with --theme. The key must be one of the highlight.js CSS class names or "default", and the value must be one or an array of Chalk styles to be applied to that token.

{
  "keyword": "blue",
  "built_in": ["cyan", "dim"],
  "string": "red",
  "default": "gray"
}

The style for "default" will be applied to any substrings not handled by highlight.js. The specifics depend on the language but this typically includes things like commas in parameter lists, semicolons at the end of lines, etc.

The theme is combined with the default theme. The default theme is still not colored a lot or optimized for many languages, PRs welcome!

Supported Languages

All languages of highlight.js are supported. Check a CI build for examples of all the different languages and their highlighting.

Contributing

The module is written in TypeScript and can be compiled with npm run build. npm run watch starts tsc in watch mode. Tests are written with mocha.

Improving language support is done by adding more colors to the tokens in the default theme and writing more tests.